CONTRIBUTION OF AUTOIMMUNE AND INFLAMMATORY RESPONSES TO NTDS Folate homeostasis is essential for a healthy pregnancy outcome. Folic acid (FA) deficiency during pregnancy has been shown to contribute to fetal demise, growth retardation, craniofacial, cardiovascular, neural tube defects (NTDs), and numerous other congenital abnormalities. Dietary supplementation with folic acid before and during gestation markedly reduces (-70%) the incidence of NTDs in humans. Given the established role for FA in preventing NTDs, we hypothesized that dietary folate stress (i.e., a folate deficiency) may, in the presence of disrupted complement factor C5a signaling and related NO-mediated processes, have deleterious consequences for neural tube formation and closure. This is a highly novel hypothesis supported by strong preliminary evidence from our laboratory leading to the inescapable conclusion that the complement system, and in particular CD88, interacts with FA metabolism to influence neural tube closure (NTC) in murine embryos. We hypothesize that under conditions of low dietary FA, C5a generated in the developing placenta and/or developing embryo releases factors(s) that promote normal NTC, thereby preventing the development of NTDs. Clearly, under certain select conditions (infection, immune suppression, altered homocysteine homeostasis, toxicant exposure, lack of anti-oxidants, others), this regulation by C5a may not occur, and could result in the development of NTDs by previously unexamined mechanisms. This is the focus of experiments in Project 3. The proposed research will provide significant support for proposed mechanisms involving post-translational modification of selected proteins interfering with normal NTC, which opens the possibility of developing highly targeted intervention strategies that modify the impact of homocysteinylation on complement release during critical stages of development. Further dissection of the role of complement factors during NTC represents yet another potential avenue for clinical intervention in high-risk pregnancies. This has broad implications for the 300,000 infants born with NTDs annually worldwide.